Author’s Note: The following article comes from a chapter in “The King Air Book, Volume I.” It has been abbreviated and simplified here to appeal to more King Air operators.
The King Air B100 model is unique, as most of our readers know, in that it is the only production model in the King Air series that is not powered by a version of the Pratt and Whitney PT6 powerplant. Instead, it is fitted with the Garrett (now Honeywell) TPE331 turboprop engine, similar to those installed on lots of King Air competitors such as Turbo Commanders, MU-2s, Conquests IIs, etc. It is a fine engine with a large following of enthusiastic fans, but it is very different in design and operation than the PT6. The intent of this article is to highlight those differences and to provide some operational tips for pilots of this rare model.
Model 100-Series History
The King Air 100 model appeared on the market in 1969. It was the first stretched King Air with a cabin that is 4 feet longer than members of the 90-series. The wing, landing gear and empennage for the 100 came from the Model 99 that had been developed a few years earlier. The 99 is the unpressurized, PT6-powered, commuter airliner that can carry up to 15 passengers. Its wing lacks the extended wingtip (that was introduced on the B90) giving it the same wingspan as the 90 and A90. However, it has a pronounced droop in the leading edge of the center section that allows it to provide a lower stall speed for a given weight. It also has a large stall fence on each side midway out between the nacelle and tip. (Later, the F90 would use the same wing shape and size but without the stall fences.)
To accommodate the 15 passengers, the 99’s fuselage is quite long and the tail needed to be designed to provide enough control and trim authority to handle a much larger CG envelope. Instead of trim tabs on the elevators, Beech went with a movable horizontal stabilizer … like that used on a Piper Cub or Cessna 180, for example. However, unlike the Cub and Skywagon, the stabilizer on the 99- and 100-series was so big that moving the jackscrew manually proved to be too difficult. Instead, a system was designed and certified that included both an electric Main and electric Standby trim motor that operate the stabilizer through a clutch/gearbox arrangement such that if one motor fails the other can still function. When one first flies a 100, it is a bit disconcerting to reach for the elevator trim wheel and find it missing! Normal trimming is accomplished through the use of dual switches on the outboard grip of the pilot’s or co-pilot’s control wheel. Standby trimming is achieved by use of two switches on the pedestal, accessible to both pilots. A trim-in-motion aural tone beeps whenever the stabilizer moves. That, too, is unusual at first but soon becomes expected and almost unnoticed.
The original “straight” 100 model had three-blade propellers, a maximum takeoff weight of 10,600 pounds and fuel capacity was a rather paltry 374 gallons. B-2 through B-89, and B-93 are the 100 serial numbers.
In 1972 the A100 replaced the straight 100, beginning with serial number B-90. For the very first time, Beech installed a four-blade propeller as standard equipment. Fuel capacity went up to 470 gallons, with a highly improved delivery system that, again for the first time, utilized an engine-driven boost pump. Maximum takeoff weight was increased to 11,500 pounds. The last A100, B-247, was built in 1979.
The very first model 100, serial number B-1, has a fascinating history. After being the flight test vehicle used in certifying the aircraft, Beech kept the airplane at the factory in Wichita and used it for additional miscellaneous flight testing. It was next used as the prototype for the A100 certification program and remained at Beech in the flight test department. Finally, in 1976, Beech removed it from the experimental category and re-certified it as a normal category A100 and it was sold to the State of Kansas. N3100K is still shown in the FAA registry. Thus, B-1 was born as a straight 100 but became an A100!
All members of the 100-series exhibit a “big-airplane” feel. They are heavier on the controls than any 90, 200 or 300-series model. They tend to decelerate rapidly in the flare and finesse is required to make consistently satisfying landings. There’s not much ground effect due to the short wings. Nevertheless, many pilots have come to prefer the solid, stable feel of the 100, A100 and B100. It is a great instrument platform when hand-flying.
Origin of the B100
In the early 1970s, when the sales of new King Airs were setting records and the production rate was at an all-time high, the Pratt & Whitney factory had a labor/management dispute that led to a long-lasting strike. The result of this protracted work stoppage and the supply of PT6 engines came to a halt. At one time, Beech had over 50 completed King Airs sitting in Wichita with paint, interior and avionics all finished but with lead weights sitting on the engine mounts (to prevent them from tipping back onto their tails) since no engines were at hand. Needless to say, Beech had a severe cash-flow problem, with so much money tied up in those airplanes and no way to collect money from the customers since the airplanes could not yet be delivered.
Frank Hedrick, the president of Beech at the time, decided that it was too risky to have such a large component of the Beechcraft product line dependent upon one sole engine supplier and he instigated an effort to provide another engine supplier for the King Air series. The TPE331 was the obvious choice of powerplant, being about the only other game in town in light turboprop engines.
About a year before the P&W strike, Beech had introduced the Super King Air 200 model. With the same cabin size as the A100 model – that had been the top-of-the-line King Air until the 200 came along – but offering a huge performance increase, most potential A100 buyers were being convinced to spend the extra dollars to order a 200 instead. Hence, Beech was seeing a dramatic reduction in the orders for A100s.
It was this fact that led Mr. Hedrick to decide the 100-series would be the first to offer the new powerplant package. By doing so, perhaps some new interest and life could be breathed into this fine segment of the King Air model line. Eventually, however, Mr. Hedrick’s plan was to offer the choice of PT6 or TPE331 engines across all branches of the King Air family tree existing at that time: the 90-series, the 100-series and the 200-series.
By the time the TPE331-powered version of the A100 – given the designation B100, of course – was finally certificated and ready for customer deliveries, two years had elapsed and the flow of PT6s was back to its historically high abundance. Although the B100 found a ready market among die-hard TPE331 advocates, it never sold nearly as well as its big brother, the 200. A contributing factor to the lack of strong sales success for the B100, in my opinion, is that the King Air sales team had been so indoctrinated into the “PT6 good, 331 bad” school of thinking that many of the salesmen and saleswomen found it very difficult to sing the praises of this different engine to their prospective buyers.
The outcome of this lack of a strong B100 market is that Beech dropped the idea of offering the alternative powerplant across the board of King Air models. Although the factory did develop and conduct flight testing on a prototype TPE331-powered version of the F90 – it was to be known as the G90 and the prototype’s serial number was LE-0, leading the factory pilots to refer to the plane as “Leo” – the program never evolved past the testing stage. I would be quite surprised to ever see another new King Air model that utilizes a version of the 331.
B100s were only delivered over an eight-year span from 1976 through 1983. The prototype started life as an A100, serial number B-205, and was given the new serial number of BE-1. The last one manufactured in 1983 was BE-137. All B100s were delivered with 715 SHP (shaft horsepower) TPE331-6-252B engines, all have a maximum gross takeoff weight of 11,800 pounds, with typical cruise speeds of about 250 knots. That speed is 15 to 20 knots faster than the realistic cruise speed of the 100 and A100. Because they have the short wingspan and the rather lowly 4.6 psid maximum differential pressure that is common to all of the 100-series, few B100s spend much time above FL220. Offering the same cabin dimensions of a 200 or 300, yet with significantly less fuel burn and rather good low-altitude speed performance, the B100 has proven to be a popular model among King Air charter operators. Also, it is much more commonly found in the eastern, rather than the western, portions of the U.S. due to its modest single-engine service ceiling.
Some B100s have been converted to the later-designed “Dash 10” version of the 331. These models exhibit increased climb and cruise performance as well as better availability of hot-section component parts. Another popular conversion is the Raisbeck Engineering modification that increases the maximum gross takeoff weight significantly.
As most of you know, the PT6 is a “free turbine” design wherein the Power Turbine (PT) that drives the propeller through the reduction gearbox is totally free and independent from the Compressor Turbine (CT) that drives the compressor. The TPE331, in contrast, is a “fixed shaft” turboprop, wherein all rotating components are fixed together and rotate simultaneously, although not necessarily at the same speed due to reduction gearing. The starter on a PT6 only turns the compressor and does not have to spin the mass of the propeller and gearbox. In contrast, the starter on the 331 must turn everything in the engine. That is why the PT6 gets by with a single battery but the B100 requires two of that same size. It also leads to huge differences in how the engines are started, operated and shutdown.
Starting the 331 is a totally different process than starting a PT6. In fact, the pilot’s left subpanel and the power quadrant are greatly changed between the A100 and B100 models. There are switches in the B100 that were never there before! Instead of Power, Propeller and Condition levers, there are Power, Speed and Fuel Cutoff & Feather levers. Because it is relatively easy to harm the engine due to improper starting procedures – and I would opine that the PT6 is much more forgiving to bad technique than the 331 – one needs to read the POH procedure thoroughly, practice it under the direction of an experienced instructor or operator, and take every care to do it properly.
For the newcomers, you need to practice the proper starting procedure thoroughly, with the battery switch off, until the steps are easy for you. It takes some coordination and practice for the fingers of the left hand to do their tasks well.
Flight Idle Fuel Flow Check
I have often discovered that the flare-for-landing characteristics of some B100s are less forgiving than desired because the Flight Idle Fuel Flow (FIFF) adjustment is set incorrectly. Perhaps in a misguided attempt to reduce engine starting temperatures, the FIFF is set too low, far below the setting desired by Beech or Garrett/Honeywell. The result is that the airplane “falls out of the sky” when power is reduced to flight idle. Here is how you, the pilot, can determine if your airplane is meeting the proper FIFF specifications:
Begin this check at 6,000 feet pressure altitude. Configure the airplane for landing – gear down, speed levers fully forward, flaps down. Trim the aircraft for 100-105 KIAS and reduce power levers to flight idle.
Passing through 5,000 feet, check for:
1,800 fpm descent rate (yes, it seems high but it’s correct!)
No adverse yaw
No Beta lights
Approximately 180 pph fuel flow per engine
Record the descent rate and the fuel flow that you observe, then add power and return to normal configuration.
If the FIFF needs to be adjusted, maintenance personnel should turn the adjusting screw on the rear of the fuel control unit clockwise to increase fuel flow (1 click = 2 pph). A very rough rule-of-thumb is that each 10 pph fuel flow change will make a 300 fpm rate-of-descent change. Realize that the FIFF setting cannot be verified properly without a flight test being accomplished!
Engine Inlet Heat
When the Engine Inlet heat switches are turned on in flight, ITT will rise momentarily then drop to a lower value than originally set. The theory here is that the initial rise is caused by the reduction of cooling airflow as air is bled from the compressor and directed to the inlet, but that the subsequent decrease in ITT is caused by the P2/T2 sensor getting warmer and directing the fuel control unit to reduce fuel flow. If desired, the power levers may then be advanced to regain the original ITT. There is a trap waiting here for you. Namely, when you leave icing conditions and turn the switches off, ITT will eventually creep well above your original setting unless power levers are retarded. Therefore, monitor ITT carefully and reduce power enough to leave a comfortable margin below the cruise ITT setting when turning off Engine Inlet heat. Remember that +5°C OAT is the maximum value at which Engine Inlet heat may be used. Leaving it on too long when in warm air may lead to compressor rub in the engine!
Ballooning with Flaps
There is a very pronounced pitch-up, or ballooning, effect when flaps are lowered on any member of the 100-series, including the B100. Here are a few suggestions:
When selecting Approach flaps while operating near the appropriate airspeed limit of 179 knots, holding the main trim switches in the nose-down direction for 3 or 4 “beeps” of the trim-in-motion aural indicator will nicely balance the pitch-up tendency.
Another method when lowering flaps to Approach is to reduce power and let the airspeed drop well below the 179-knot limit without trimming, so that the nose is getting heavy, then lower the flaps. Presto! You are right back in trim!
When changing from 30% to 100% flaps for landing, you may wish to do so in steps … 60, 80, 100%. Instead of trimming forward (nose down) as they extend, stiff arm the control wheel to maintain the visual glide path and be patient. As the drag takes effect, airspeed will decrease and you will find yourself once again nicely trimmed. During this time do not rush to reduce power. The airspeed will very rapidly decay with full flaps if power is too low! The same torque that gave a stabilized ILS approach with 30% flaps will yield about the same descent angle with 100% flaps at landing speed.
Fuel Venting
Sometimes B100s (and E90s, F90s, A100s, 200-series and 300-series that have basically the same fuel system) have been known to vent an awful quantity of fuel onto an FBO’s ramp or hangar floor. There is a step pilots can take that almost guarantees this event will never happen.
When fuel is being transferred from the auxiliary tank to the main tank, it transfers at a rate greater than the rate at which the engine is burning the fuel. Consequently, the main tank overfills and builds up enough pressure that a relief valve should vent excess fuel from the main tank back into the aux tank. (Although it should do that, sometimes a portion of the excess is vented overboard!) When auxiliary fuel transfers to an already-full main tank, that main tank becomes pressurized or overstuffed with fuel. If ever there is a time when fuel venting will occur, this is it.
I suggest, therefore, that you delay turning on the Aux Transfer switches until leveling off at cruise altitude. Doing so will allow the main tanks to come down from their full condition and hence provide some room so that the aux fuel may now be accepted without causing an overstuffed condition.
When conducting wing-bending analyses, the designers assume that the main tanks will be full if the aux tanks contain fuel. That’s why the “Limitations” tells you to fill the auxes last and use them first. Nonetheless, taking out 100 or 200 pounds of fuel from the mains before transferring the auxes will not be enough to cause bending concerns unless perhaps you are loaded right up to the maximum zero fuel weight limit. In routine passenger-carrying operation that is very rarely the case.
The C100
Bet you have never heard of this King Air model, have you? In 1976, Beech decided to add enough power to the A100 to have it perform as well or better than the B100. They accomplished this by replacing the 680 SHP PT6A-28 engines with the 750 SHP PT6A-135 engines, the same engine that was to be used on the F90. Since this was such a simple change (so they thought!) Beech began building C100s before the experimental flight testing was completed. BF-1 was the first serial number and they built eight of them, through BF-8. Well, too much of a tendency toward tail flutter was uncovered at the higher speeds these engines provided. Rather than take the time and effort and money to redesign and strengthen the tail assembly, the decision was made to shelve the idea and to convert the eight undelivered C100s back into A100s. If one looks closely inside the cowl of the last eight A100s, one will find a “BF” serial number alongside the “B” number!
Summary
Fewer members of the 100-series branch of the King Air family tree have been produced than any of the other branches. Even the latest 100-series model is now almost 40 years old. For those seeking the same large cabin of the 200 or 300 and yet for a price that is less than many used 90s, the 100-series has developed a devoted following. They are solid, pleasant-handling, fun, flying machines.
King Air expert Tom Clements has been flying and instructing in King Airs for over 50 years and is the author of “The King Air Book” and “The King Air Book II.” He is a Gold Seal CFI and has over 23,000 total hours with more than 15,000 in King Airs. For information on ordering his books, contact Tom direct at twcaz@msn.com. Tom is actively mentoring the instructors at King Air Academy in Phoenix.
If you have a question you’d like Tom to answer, please send it to Editor Kim Blonigen at editor@blonigen.net.